In recent years, plasma chemical vapor deposition and photochemical vapor deposition have come to be highlighted as methods of forming films on substrates. These processes reflect the trend toward utilizing low temperatures in producing semiconductor devices including integrated circuits.
In photochemical vapor deposition (chemical vapor deposition, which will be referred to as CVD hereafter), light energy such as a laser beam and an ultraviolet light is used as an energy source for CVD. An excimer laser or a carbon dioxide gas laser is generally employed as the laser, while a low-pressure mercury lamp, a high-pressure mercury lamp, or a deuterium lamp is used as an ultraviolet light source.
FIG. 4 is a cross-sectional view schematically illustrating a conventional optical CVD apparatus which is applied to the above-described method, as disclosed in, for instance, Japanese Patent Laid-Open No. 152023/1985. In the drawing, the conventional optical CVD apparatus comprises the following components or substances: a reaction vessel 1 constituting a reaction chamber la; a substrate 2 on which a film is formed; a fixing base 3 for mounting the substrate thereon; a heater 4 for heating the substrate on the fixing base 3; a reaction gas 5 such as a silane gas; a post-reaction gas 6; a reaction gas supplying port 7; a gas discharge port 8; light transmissive windows 9 formed of a light transmissive material; a carbon dioxide gas laser oscillator 10; an optical system 11 for reducing the diameter of a carbon dioxide gas laser beam; a carbon dioxide gas laser beam 12 generated by the laser oscillator 10 and used to excite and decompose the reaction gas; and a damper 13 for absorbing the carbon dioxide gas laser beam which has passed through the reaction chamber.
In this apparatus, when the silane gas 5 is supplied from the supply port 7 to the reaction chamber 1a, the silane gas 5 is excited and decomposed by the carbon dioxide gas laser beam 12 which enters through the transmissive window 9 after it is generated by the carbon dioxide gas laser oscillator 10 and its beam diameter is then reduced by the optical system 11. The reason for this is that resonance absorption takes place at a wavelength of 10.59 .mu.m of the carbon dioxide gas laser. A reaction product obtained as a result is deposited on the substrate 2 heated to a low temperature by the heater 4, and an amorphous silicon film is formed on the substrate 2. The post-reaction gas 6 is discharged through the discharge port 8. The carbon dioxide gas laser beam 12 which has passed through the reaction chamber 1a is absorbed by the damper 13.
With the conventional semiconductor producing apparatus, it is possible to form an amorphous silicon film on a substrate by decomposing the silane gas by the carbon dioxide gas laser beam, as described above. However, the type of film formed is disadvantageously restricted to the amorphous silicon film, and it is difficult to form a silicon oxide film or a silicon nitride film by using the above-described apparatus since oxygen, nitrogen suboxide, nitrogen, or ammonia which is supplied by being added to the silane gas is difficult to decompose by the carbon dioxide gas laser.
Accordingly, it is a primary object of the present invention to provide a semiconductor producing apparatus which is capable of forming a silicon oxide film and a silicon nitride film in addition to an amorphous silicon film and which is capable of forming the amorphous silicon film at a high speed as compared with a conventional apparatus, thereby overcoming the above-described drawback of the prior art.
Another object of the present invention is to provide a semiconductor producing apparatus which is capable of controlling a film forming speed during film formation, thereby making it possible to obtain a uniform distribution of film thickness during film formation.
Still another object of the present invention is to provide a semiconductor producing apparatus which is capable of rendering active the surface of a substrate and a film surface on which active species are deposited consecutively during film formation, thereby making it possible to form a dense film on the substrate.